Insulator



A. O. AUSTIN June 4, 1929.

INSULATOR Original Filed Dec. 6, 1920 in m f/YVE/vra Md (0. M

Patented June 4, 1929.

UNITED STATES PATENT OFFICE.

ARTHUR O. AUSTIN, OF BARBERTON, OHIO, ASSIG-NOR, BY MESNE ASSIGNMENTSyTOTHE OHIO BRASS COMPANY, OF MANSFIELD, OHIO, A CORPORATION 01 NEW JERSEY.

INSULA'IOR.

Original application illed December 6, 1920, Serial No. 428,488. Dividedand this application filed December 4, 1924.

This invention relates to electrical insulators, and especially toinsulators for high voltages, and has for its object improveddistribution of electrostatic flux and the provi- 5 sion of insulatorswhich shall be of improved construction and operation;

The invention is exemplified in the combination and arrangement of partsshown in the accompanying drawings and described in the followingspecification, and it is more particularly pointed out in the appendedclaims.

This is a divisionof application, Serial No. 428,438, filed Dec. 6,1920.

In the drawing, the figure is an elevation of one end of an insulatorpartly in section showing one form of the invention.

In high tension insulators where two conductors of different potentialsare separated from one another by an insulating member,

it is well known that an electrostatic field is present in which thelines of force extend through the insulator and the surrounding mediumfrom one of the conductors to the other. Other conditions being equalthese lines of force are most closely concentrated at the portions ofthe insulated conductors which are nearest to one another. The lines offorce also concentrate at restricted projections or points formed uponthe con notors.

When insulators or dielectrics are worked at high pressures orpotentials the resulting high electrostatic density may set up a stressof such magnitude that it will damage the dielectric. This stress may beset up around a conductor imbedded in a solid die ectric or around aconducting surface which operates in a medium, such as air, oil, wax, orother medium. When the conducting surface operates in air, corona orbrush discharge may occur at a fairly low voltage, particularly wherethe conductor has a sharp edge or point. If corona or brush dischargeoccurs at normal frequency, say 60 cycles, and an electrical stress athigh frequency is imressed on the electrodes, the current will beincreased in the streamer or brush discharge. Since the resistance ofthe streamer drops ofl very rapidly with an increase in the cur- SerialNo. 753,795.

rent it is seen that where the frequency is high the current may be verymaterially increased. This increase in current lowers the resistance inthe streamer permitting the streamer to flow out further from theelectrode. This increase in distance increases the capacitance of thestreamer and permits more current to flow. The increased current in turnstill further lowers the resistance in the streamer so that it extendsstill further. Where a persistent wave at high frequency is applied,such as in wireless work, a comparatively small voltage will cause thestreamer tobuild out several feet once it is started. This streamer mayarc to ground or absorb considerable energy or damage any insulatorwhich may be near the surface which discharges.

In wireless work where a high frequency generator is used, or theequivalent, the point of brush discharge from a conducting surfacelimits the voltage which may be used. If this discharging surface iscovered by a dielectric having greater strength than the air, it will bepossible to operate at a higher voltage or stress, since a streamer,which will grow to serious proportions, is prevented. It will be seenthat where this is the condition and a strong dielectric is used tocover the surface which has greatest tendency to discharge, a higheroperating voltage may be used.

If a conducting surface has a tendency to discharge, the bringing ofanother surface charged with the same potential near will screen thefirst surface or reduce part of the concentration of stress. Ihe addedsurface forms a parallel path or circuit for the electrostatic flux andhence reduces the amount of flux emanating from the original surface.Where the screening surface is insulated it may be placed in a strongerfield without danger of discharging. This will permit it to be so placedthat it will greatly reduce the concentration of flux from someuninsulated surface. This insulated screen or shield may be effectivelyused to set up a better electrical gradient in the insulator orsurrounding mediam and permits operation at a higher potential withoutsetting up streamers on the metal parts of an insulator or a chargesurface with which it is'used.

The above is applicable to high tension lines for there is often astrong tendency for the line to are to ground at the insulator. Thistendency to are is greatly aggravated by surges on the system producedby resonant arcing ground, switching surge, poor wave or electricaldischarge, such as lightning. Any condition such as those named abovethat produces a high voltage wave or series of waves in the line will,of course, increase the tendency to arcing at the time of increasedvoltage. The starting up or slowing down of a generator excited andconnected to a parallel circuit may set up a resonant condition andcause arcing of insulators from streamers which develop in the mannerdescribed.

In the form of the invention shown in the drawing, an insulator 29 isprovided with an end cap 30 and a series of external flux distributingmembers 31. These members comprise supports 32 which carry thedistributing members 31. The members 31 are composed ofdielectricmaterial having a central opening 33 internally coated with a metalliccovering 34 from which the lines of force emanate. The coat-ing 34 maybe brought into direct contact with the support 32, or for highpotential work the cement will afford sufiicient conductivity betweenthe two parts. It will be apparent that the covering 34 is surroundedwith the insulating material of the member 31, so that any tendency todischar e along the lines of force emanata ing from t e covering 34 isprevented by the insulating material. tion of the shield or flux rodrelieves the terminal portion of the insulatin member for the flux rodof dangerous surface charging currents because of the resistance itoffers to such currents and permits operation at high voltages. Where aconstruction of this kind is used a bug, raindrop or other projection isnot so likely to cause a burr or are to form on the insulator shield aswould be the case if the surface of the shield were of conductingmaterial. This is due to the fact that the insulation limits the surfacecurrents. This is particularly important in radio insulators used on apersistent wave.

The flux control members may be provided with ribs 35 added to themembers 31 to break up the surface into small sections and limit thecharging current in case streamers start. The ribs keep down thecharging current in the small streamers by cutting the surface up intosmall sections. Where streamers start the resistance decreases and thelength of the streamers increase as the current increases. Limiting thecurrent in any streamer is then of particular advantage.

The external insula I claim 1. An insulator comprising a bar ofdielectric material, a supporting cap secured to one end thereof, metalpins mounted on said cap and spaced about the periphery thereof andextending therefrom in the direction of the length of said bar andinclined outwardly from said bar, and members of dielectric materialhaving internal openings therein secured to the extremities of saidpins, said openings having the inner surfaces thereof provided with acoating of conducting material and having the ends of said openings awayfrom said pins closed to form a completecovering of dielectric materialfor the conductors consisting of said pins and coatmgs.

2. An insulator comprising a bar of dielectric material, a cap securedto said bar, pins pro ecting outwardly from said cap and in thedirection of the length of said bar, hollow dielectric members supportedon the ends of said pins, said members having the inner surface thereofcoveredwith a coating of conducting material and having the ends thereofaway from said pins enlarged to provide increased insulation at the endsof said memers.

3. An insulator comprising a bar of dielectric material, a cap fixed atone end of said bar, pins projecting outwardly from said cap in thedirection of the length of said bar, tubular dielectric members havingopen ends mounted on said pins and having the ends thereof opposite saidpins enlarged and closed, and conducting material within said tubulardielectric members connected with said pins.

4. An insulator comprising an elongated bar of dielectric material, acap secured to one end of said bar, a plurality of pins projectingoutwardly at an angle away from said cap and forwardly in the directionof said bar, and hollow members of dielectric material eachhaving oneend open and mounted on'said pins and having its opposite end closed andenlarged, conductingmaterial disposed within said members andelectrically connected with said pins, and ribs formed on the outersurfaces of said members to divide said surfaces into sections.

5. In combination,-an insulator bar, a cap secured to one end of saidbar and a plurality of flux screens mounted on said cap and disposedabout said bar in spaced relation to one another, each screen comprisinga conductor member extending from said cap outwardly and along said bar,and a covering of dielectric material disposed over the end of each ofsaid conductor members.

6. In combination, an elongated bar of dielectric material, a fittingsecured to one end of said bar, and 'a flux screen comprising aplurality of conductor members secured to said fitting and extendingoutwardly therelfrom and along said bar, hollow dielectric membershaving open ends disposed over the ends of said conductor membersrespectively and having the ends extending away from said conductormembers, closed, conducting material within said hollow dielectric mem-

